https://github.com/keiichiw/padding-detector

Detect implicit paddings in C structs and unions
https://github.com/keiichiw/padding-detector

Last synced: 12 days ago
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Detect implicit paddings in C structs and unions

• Host: GitHub
• URL: https://github.com/keiichiw/padding-detector
• Owner: keiichiw
• License: mit
• Created: 2020-04-25T00:46:10.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2022-06-09T08:09:12.000Z (over 2 years ago)
• Last Synced: 2024-11-08T01:14:26.288Z (2 months ago)
• Language: Rust
• Homepage:
• Size: 15.6 KB
• Stars: 3
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# padding-detector

A command line tool to detect implicit paddings that will be added in C structs and unions.

## Usage

```sh

$ cargo build --release

$ cat ./examples/simple.h

#include

struct test1 {

        uint8_t a;

        // <3-byte padding>

        uint32_t b;

        uint64_t c;

        uint8_t d;

        // <7-byte padding>

};

union test2 {

        uint64_t a;

        char b[9]; // followed by 7-byte padding

};

$ ./target/release/padding-detector ./examples/simple.h

Checking `struct test1` (size=24)...

 Warning: Implicit padding was found: sum of fields: 14, struct size: 24

   Found: 3-byte padding before "b"

   Found: 7-byte padding at the end

Checking `union test2` (size=16)...

   Found: 7-byte padding is inserted

```

## How it works

The work flow consists of the following three steps:

1. Generates Rust FFI bindings to C structs in the given header by [bindgen].

2. Adds functions in the generated Rust file to check paddings.

3. Executes the generated Rust program in 2.

You can see the generated Rust codes by the following command:

```

# You'll find './out/bindings.rs' and './out/generated.rs' for step 1 and 2, respectively.

$ ./target/release/padding-detector ./examples/simple.h -o ./out/

```

The reason why it generates Rust bindings instead of processing C directly is it's easy to process

Rust's ASTs thanks to [syn].

[bindgen]: https://github.com/rust-lang/rust-bindgen

[syn]: https://github.com/dtolnay/syn

## Requirements

This tool depends on `libclang`, on which `bindgen` depends.

See [bindgen's doc](https://rust-lang.github.io/rust-bindgen/requirements.html).